The present invention relates to a linear guide, particularly relates to a linear guide used in industrial machines etc. Further, the present invention also relates to a linear guide that is suitably used in a stepper etc. used in a semiconductor element fabrication process.
Conventionally, as a linear guide used in general, there is known one, for example, which includes a guide rail 1 extending in the axial direction thereof and a slider 2 assembled to the guide rail 1 so as to cross over the rail, as shown in FIG. 1. In such a linear guide, rolling element rolling grooves 3, 3, 3, 3 are formed along the axial direction thereof at both side surfaces 1b, 1b of the guide rail 1.
As shown in FIGS. 1 and 2, the slider 2 is formed by a slider main body 2A and end caps 2B, 2B attached to the both end portions of the main body along the axial direction thereof. The slider main body 2A has rolling element rolling grooves 4, 4, 4, 4 opposing to the rolling element rolling grooves 3, 3, 3, 3 of the guide rail 1 at the inner side surfaces of both sleeve portions 6, 6, respectively, and rolling element return paths 11, 11, 11, 11 penetrating the thick portions of the sleeve portions 6, 6 in the axial direction thereof (see FIG. 2). These opposed rolling element rolling grooves 3, 3, 3, 3 and 4, 4, 4, 4 form rolling element rolling paths 10, 10, 10, 10.
As clear from FIG. 3 showing the plan view of the linear guide in which the slider 2 is partially cut-away, the end caps 2B, 2B have curved paths 12 each for communicating the rolling element rolling path 10 and the rolling element return path 11 disposed in parallel to each other. The rolling element rolling path 10, the rolling element return path 11 and the curved paths 12 at the both ends thereof form a rolling element circulation path. Many rolling elements 5 formed by steel balls, for example, are filled within the rolling element circulation path.
The slider 2 assembled to the guide rail 1 moves smoothly along the guide rail 1 through the rolling operation of the rolling elements 5 within the rolling element rolling paths 10, and the rolling elements 5 circulate endlessly while rolling within the rolling element circulation path of the slider 2.
Side seals 7 for sealing the openings of gaps between the guide rail 1 and the slider are attached to the both end portions (the end surfaces of the respective gaps 2B) of the slider 2. A symbol 8 of FIG. 1 depicts a grease nipple.
In such a conventional linear guide, the surface roughness of the rolling element rolling grooves 3, 4 is set in a manner that the average roughness Ra along the center line thereof is more than 0.20 xcexcm by the grinding finishing process etc.
However, the aforesaid conventional linear guide has a problem that abrasion (initial abrasion) due to the shake-down among the members occurs at the initial stage of the usage (upon running of several km), so that the sliding resistance likely reduces and powder of the members due to the abrasion is likely generated.
Further, when the aforesaid linear guide is used in the working machine, since the sliding resistance changes with the lapse of time as described above, there arises a problem that the accuracy of the processing performed by using the working machine is badly influenced.
Further, since the sliding resistance changes in accordance with the moving speed of the slider 2, when the cutting speed changes in the processing (for example, arc cutting etc.) performed by the working machine, there also arises a problem that the resistance value varies and so the processing with high accuracy can not be realized.
In addition to this, conventionally, the stepper (micro projection exposure apparatus) used in the semiconductor element fabrication process employs high-energy light such as excimer laser etc. as a light source. The linear guide for the stepper is usually lubricated by fluoro grease. The fluoro grease is a mixture of a base oil composed of liquid fluorinated polymer oil and a thickening agent composed of solid fluorinated polymer. Although the liquid fluorinated polymer oil is not necessary limited, there may be used perfluoro-polyether (hereinafter referred to as xe2x80x9cPFPExe2x80x9d), a telomer of trifluoro-ethylene, fluoro-siliconepolymer, or the like. As the solid fluorinated polymer, there may be used polytetrafluoro-ethylene (hereinafter referred to as xe2x80x9cPTFExe2x80x9d), a copolymer of tetrafluoro-ethylene and hexafluoro-propene, a copolymer of tetrafluoro-ethylene and perfluoro-propylvinylether, a mixture of these polymers, or the like. This is because, it is not preferable to use the stepper in such a circumstance where dust is likely generated. Further, when light with a high energy is irradiated on general grease (lithium system or urea system), vapor is generated from the grease and adhered to a lens, so that the lens is required to be exchanged frequently.
As shown in FIG. 4, the linear guide is configured by a guide rail 1, a slider 2 and rolling elements 3. The guide rail 1 has rolling element rolling grooves 11 extending in parallel to each other along the longitudinal direction thereof at both side surfaces 1b thereof. The slider 2 is engaged with the guide rail 1 so as to cross over the rail in a manner that the both inside surfaces 2a of the slider 2 are disposed to oppose to the both side surfaces 1b of the guide rail 1, respectively. Rolling element rolling grooves 12 are formed at the both inside surfaces 2a of the slider 2 so as to oppose to the rolling element rolling grooves 11 of the guide rail 1, respectively. The linear guide is arranged in a manner that when the rolling elements 3 roll along rolling paths formed by the both rolling element rolling grooves 11, 12, the slider 2 slides along the guide rail 1.
Although a general linear guide has two pairs of rolling paths, that is, four columns of rolling paths, a small-sized linear guide for a stepper etc. has a pair of rolling paths, that is, two columns of rolling paths as shown in this figure. In this case, when a preload is applied, since the rolling element contacts with the rolling path at four points, there,arises a problem that differential slip becomes large. Further, it is required to make the friction small so as to drive the linear guide under the electronic control Thus, since the exposed thread due to the preload is suppressed to about 1 xcexcm, a setting preload may not be held due to a slight abrasion. If the setting preload is not held, the accuracy of the linear guide degrades.
When the rolling element rolling grooves of the linear guide are lubricated by the fluoro grease which is deteriorated in lubrication characteristics as compared with general grease, initial abrasion of the linear guide occurs in a relatively short time.
Further, in the case of using a linear motor as the driving apparatus in order to attain a high acceleration and deceleration, the changes of the friction force becomes larger and so oscillation may occur.
Thus, in the case of lubricating the rolling element rolling grooves of the linear guide (particularly, a small-sized linear guide) by the fluoro grease, since the setting preload is not likely held at the time of the initial abrasion, there arises a problem that the accuracy of the linear guide is apt to degrade in a short time.
Accordingly, an object of the invention is to solve the problems of the aforesaid conventional linear guide. It is an object of a first aspect of the present invention to provide a linear guide in which reduction of a sliding resistance and generation of powder due to the abrasion caused by the initial abrasion are not easily occurred.
In order to solve the aforesaid problems, the first aspect of the present invention is configured in the following manner. That is, in the linear guide which includes a guide rail having at its outer surfaces rolling element rolling grooves extending in an axial direction thereof, a slider which is assembled to the guide rail and has rolling element rolling grooves opposing to the rolling element rolling grooves of the guide rail, and a plurality of rolling elements filled within rolling element rolling paths formed by both the rolling element rolling grooves of the guide rail and the slider so as to roll freely therein. In the linear guide, at least a part of the rolling element rolling grooves of the guide rail and the slider is set to have an average roughness Ra along a center line thereof of 0.20 xcexcm or less.
According to such a configuration, since the surface of the rolling element rolling grooves is smooth, the reduction rate of the sliding resistance due to the initial abrasion can be suppressed to 10% or less and further the generation of powder due to the abrasion can also be suppressed. Thus, since the time-lapse change of the sliding resistance is small, the processing with high accuracy can be realized when the linear guide is used in the working machine. Further, since the change of the sliding resistance in accordance with the moving speed of the slider is small, even if the grinding speed changes in the processing (for example, the arc cutting processing etc.) using the working machine, the degree of the change of the sliding resistance is small and so the processing with high accuracy can be realized.
Further, since the abrasion coefficient at the time of the rolling of the rolling elements is low, the sliding resistance at the initial stage can be made small while maintaining the efficiency of the rigidity etc. to almost the same degree. Furthermore, noise caused upon usage of the linear guide (running of the slider) can be made small.
Such effects can be easily obtained, in particular, when the rolling element contacts with the rolling element rolling path at four points.
In the above-mentioned linear guide, it is advantageous to comprise fluoro grease for lubricating the rolling element rolling grooves of the guide rail and the rolling element rolling grooves of the slider.
In addition, in the above-mentioned linear guide, said surface may be subjected to precise finishing process after grinding process. The precise finishing process can be selected from the group essentially consisting of super finishing process, honing process, lapping process, polishing process, buffing process, and tape process (polishing process using a polishing tape).
Moreover, the invention has been made in view of the aforesaid problems of the prior art. It is an object of a second aspect of the present invention to hold the accuracy of a linear guide for a long time even when the linear guide is lubricated by the fluoro grease.
In order to solve the aforesaid problem, a linear guide according to the second aspect of the present invention is configured by a guide rail having at its outer surfaces rolling element rolling grooves extending in parallel to each other along a longitudinal direction thereof, a slider engaged with the guide rail so as to cross over the guide rail and having rolling element rolling grooves opposing to the rolling element rolling grooves of the guide rail at its inner surfaces disposed so as to oppose to the outer surfaces, respectively, and rolling elements, whereby the rolling elements roll along rolling paths formed by the opposed rolling element rolling grooves to thereby slide the slider along the guide rail, and wherein the rolling element rolling grooves of the guide rail and the rolling element rolling grooves of the slider are lubricated by fluoro grease and subjected to precise finishing process after grinding process so that surface roughness (Ra) of the rolling element rolling grooves is equal to or less than 0.20 xcexcm.
As concrete examples of the precise finishing process, there are the super finishing process, the honing process, the lapping process, the polishing process, the buffing process, the tape process (polishing process using a polishing tape) etc.